Mergers and Acquisitions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Nov. 22, 2019	Aug. 20, 2018	Apr. 05, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total Assets				$ 16,425,610	$ 15,720,112
Old Line [Member]
Business Acquisition [Line Items]
Total Assets	$ 3,000,000
Portfolio loans, net of unearned income	2,500,000
Securities	182,171
Value of acquisition	$ 493,952
Closing stock price	$ 36.75
Number of shares issued for acquisition	13,351,837
Business acquisition, fair value	$ 3,300
Goodwill acquired	231,814			231,800
Purchase price allocation in core deposit intangible	32,899
Merger related expense				$ 6,500	13,200
Cash consideration for outstanding shares	16
Farmers Capital Bank Corporation [Member]
Business Acquisition [Line Items]
Total Assets		$ 1,600,000
Portfolio loans, net of unearned income		1,000,000
Securities		239,321
Value of acquisition		$ 428,901
Closing stock price		$ 49.40
Number of shares issued for acquisition		7,920,387
Goodwill acquired		$ 223,304
Purchase price allocation in core deposit intangible		39,992
Merger related expense					$ 3,200	$ 12,400
Cash consideration for outstanding shares		37,634
First Sentry Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Total Assets			$ 704,800
Portfolio loans, net of unearned income			447,300
Securities			142,903
Value of acquisition			$ 108,322
Closing stock price			$ 42.96
Number of shares issued for acquisition			2,498,761
Goodwill acquired			$ 67,699
Purchase price allocation in core deposit intangible			8,078
Merger related expense						$ 5,500
Cash consideration for outstanding shares			975
Community Banking [Member] | Old Line [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible	$ 32,900
Community Banking [Member] | Farmers Capital Bank Corporation [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible		37,400
Community Banking [Member] | First Sentry Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible			$ 8,100
Trust And Investment Services [Member] | Farmers Capital Bank Corporation [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Purchase price allocation in core deposit intangible		$ 2,600